Effects of carbohydrate supplementation on aerobic exercise performance during acute high altitude exposure and after 22 days of acclimatization and energy deficit

Abstract

Background: The ergogenic effects of supplemental carbohydrate on aerobic exercise performance at high altitude (HA) may be modulated by acclimatization status. Longitudinal evaluation of potential performance benefits of carbohydrate supplementation in the same volunteers before and after acclimatization to HA have not been reported. Purpose: This study examined how consuming carbohydrate affected 2-mile time trial performance in lowlanders at HA (4300 m) before and after acclimatization. Methods: Fourteen unacclimatized men performed 80 min of metabolically-matched (~1.7 L/min) treadmill walking at sea level (SL), after~5 h of acute HA exposure, and after 22 days of HA acclimatization and concomitant 40% energy deficit (chronic HA). Before, and every 20 min during walking, participants consumed either carbohydrate (CHO, n = 8; 65.25 g fructose + 79.75 g glucose, 1.8 g carbohydrate/min) or flavor-matched placebo (PLA, n = 6) beverages. A selfpaced 2-mile treadmill time trial was performed immediately after completing the 80-min walk. Results: There were no differences (P > 0.05) in time trial duration between CHO and PLA at SL, acute HA, or chronic HA. Time trial duration was longer (P < 0.05) at acute HA (mean ± SD; 27.3 ± 6.3 min) compared to chronic HA (23.6 ± 4.5 min) and SL (17.6 ± 3.6 min); however, time trial duration at chronic HA was still longer than SL (P < 0.05). Conclusion: These data suggest that carbohydrate supplementation does not enhance aerobic exercise performance in lowlanders acutely exposed or acclimatized to HA.

Carbohydrate Supplementation and the Influence of Breakfast on Fuel Use in Hypoxia

“…Interestingly, carbohydrate supplementation had no effect on 3 km time trial performance. This is in agreement with Bradbury et al (17) who observed no difference in time trial performance…”

“…As such, it seems likely that muscle glycogen concentration did not reach a critical threshold (< 70 mmol•kg -1 wet weight) in which it may be expected calcium release from the sarcoplasmic reticulum is impaired, and subsequently peak power output reduced (41). This hypothesis may also explain the null findings observed by Bradbury et al (17), as they utilised similar experimental design. Despite the novel findings reported in this study, several limitations must be acknowledged.…”

“…However, later research by the same group observed no difference in time trial performance after carbohydrate supplementation in fed participants (albeit in moderate altitude residents) (16). In addition, recent literature has demonstrated no effect of carbohydrate supplementation on time trial performance in acute or chronic hypoxia when fasted and in energy deficit respectively (17). The effects of carbohydrate supplementation in both the fasted and fed state are yet to be determined using a within-study design, and an ecologically valid mode of exercise in relation to the severity of hypoxia.…”

The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude

“…In the end of the stay, SpO 2 following exercise remained unchanged or increased by 3% [ 63 , 76 , 77 ]. In the studies lasting from seven to 22 days, SpO 2 declined by −15% to −23% during exercise tests at acute hypoxia [ 60 , 66 , 68 , 78 ]. In these studies, the rise in SpO 2 during acclimatization ranged from 2% to 10%.…”

“…Exercising HR at acute altitude exposure increased by 11 bpm to 38 bpm in six out of seven studies when compared to sea level. In the remaining two studies, reporting either 55% slower time trial durations [ 78 ] or significant reductions in mean power [ 77 ], exercising HR during acute altitude exposure declined in a range of −1 bpm to −7 bpm. In those studies, showing a primary increase in HR during the first exercise test, the reduction in exercising HR ranged from −4 bpm to −8 bpm [ 60 , 63 , 66 , 76 ], still being elevated compared to sea level.…”